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Appendix D Measures Against Noise
To improve noise immunity, take measures against noise as follows:
Noise Measures for V
When noise falling below the rated voltage is input, an IC malfunction may occur. If desired operations cannot
be achieved, take measures against noise on the circuit board, such as designing close patterns for circuit board
power supply circuits, adding noise-filtering decoupling capacitors, and adding surge/noise prevention compo-
nents on the power supply line.
For the recommended patterns on the circuit board, see "Mounting Precautions" in Appendix.
Noise Measures for #RESET Pin
If noise is input to the #RESET pin, the IC may be reset. Therefore, the circuit board must be designed properly
taking noise measures into consideration.
For the recommended patterns on the circuit board, see "Mounting Precautions" in Appendix.
Noise Measures for Oscillator Pins
The oscillator input pins must pass a signal of small amplitude, so they are hypersensitive to noise. Therefore,
the circuit board must be designed properly taking noise measures into consideration.
For the recommended patterns on the circuit board, see "Mounting Precautions" in Appendix.
Noise Measures for Interrupt Input Pins
This product is able to generate a port input interrupt when the input signal changes. The interrupt is generated
when an input signal edge is detected, therefore, an interrupt may occur if the signal changes due to extraneous
noise. To prevent occurrence of unexpected interrupts due to extraneous noise, enable the chattering filter cir-
cuit when using the port input interrupt.
For details of the port input interrupt and chattering filter circuit, see the "I/O Ports" chapter.
Noise Measures for UART Pins
This product includes a UART for asynchronous communications. The UART starts receive operation when it
detects a low level input from the SINn pin. Therefore, a receive operation may be started if the SINn pin is set
to low due to extraneous noise. In this case, a receive error will occur or invalid data will be received.
To prevent the UART from malfunction caused by extraneous noise, take the following measures:
• Stop the UART operations while asynchronous communication is not performed.
• Execute the resending process via software after executing the receive error handler with a parity check.
For details of the pin functions and the function switch control, see the "I/O Ports" chapter. For the UART con-
trol and details of receive errors, see the "UART" chapter.
Noise Measures for Input Pins Connected to Signal with High Driving Capability Such
As Power Supply
There is a possibility of a large current flow into the pins that are directly connected to a power supply or an
output of a device with high driving capability if noise is input to those pins. To prevent this, connect a 30 W or
more pin protection resistor to the pins in series. The resistance value should be determined by evaluating it on
the mounting board.
When connecting a power supply directly to the VREFA pin, insert a 100 W resistor in series. This resistance
does not affect the A/D converter characteristics.
S1C31D41 TECHNICAL MANUAL
(Rev. 1.1)
, V
, and V
Power Supply Pins
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DDQSPI
SS
Seiko Epson Corporation
APPENDIX D MEASURES AGAINST NOISE
AP-D-1
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